Recently, in conjunction with increasing performance of vehicles, there are strong demands that pneumatic tires perform both steering stability on a dry road surface and steering stability on a wet road surface to a high degree while running at a high speed.
Generally, as a method of improving steering stability on the wet road surface, drainage is ensured by disposing many inclined grooves and sipes on a tread surface of a tire. However, with this method, because a rigidity of a land portion formed on the tread surface decreases, there is a problem where it becomes difficult to ensure steering stability on the dry road surface.
With regard to such a problem, a pneumatic tire that performs both steering stability on the dry road surface and steering stability on the wet road surface to a high degree is known (Japanese Unexamined Patent Application Publication No. 2010-215221A).
This pneumatic tire has four main grooves extending in a straight shape in a tire circumferential direction in a ground region of a tread surface and has five land portions partitioned by the main grooves on the tread surface.
A groove width of the main groove positioned nearest to one side in a tire width direction from among these four main grooves is formed narrower than a groove width of any of the other three main grooves, and a ratio Wmax/Wout between a maximum groove width Wmax of the three main grooves and a groove width Wout of the main groove positioned nearest to the one side in the tire width direction is set as 2.0 to 3.0.
Additionally, only the land portion positioned nearest to the one side in the tire width direction from among the five land portions is formed in a block column by being partitioned by inclined grooves disposed at predetermined intervals in the tire circumferential direction, and the other four land portions are formed as ribs that continue in the tire circumferential direction.
A ratio Sin/Sout between a groove surface area ratio Sin of another side in the tire width direction and a groove surface area ratio Sout of the one side in the tire width direction with a tire equator in the ground contact region as a center is set as 1.25 to 1.35, and regarding the groove surface area ratios in the ground contact region of the three land portions which do not include the land portion nearest to the other side in the tire width direction and the land portion nearest to the one side in the tire width direction from among the five land portions, the groove surface area ratio of another side in the tire width direction is larger than the groove surface area ratio of one side in the tire width direction when a center line of each land portion is defined as a boundary.
While the known pneumatic tire described above can provide both steering stability on the dry road surface and steering stability on the wet road surface at the high dimension, situations are increasing where an additional improvement of uneven wear resistance of the pneumatic tire is still further demanded so the pneumatic tire can be used continuously for a longer period without a tire exchange or a tire rotation. With the known pneumatic tire described above, improvement of uneven wear resistance is not considered.